The present invention relates generally to detecting anomalies (e.g., a broken rotor bar) in the rotor of induction machines, such as alternating current (AC) induction machines
AC induction machines, or motors, are used in a wide array of applications and processes. An AC induction machine typically includes a stationary portion, a “stator,” and a rotating portion, a “rotor.” In a 3-phase AC machine, power is applied to the stator to induce a magnetic field, causing the rotor to turn and generate mechanical energy. The stator may include any number of “windings,” or wound poles that carry the current necessary to induce the magnetic field. These windings may also be characterized by the “turns” in the windings.
An anomaly (e.g., broken rotor bar(s), failure in an end ring, etc.) in the rotor, or rotor anomaly, is one of the predominant failure modes of an AC induction machine. Rotors are typically manufactured either from aluminum alloy, copper or copper alloy or copper windings. Large machines generally have rotors and end-rings fabricated out of these materials, whereas motors with ratings less than a few hundred horsepower generally have die-cast aluminum alloy rotor cages. Some induction machines also use copper windings and slip ring and brush arrangements. Rotor anomaly rarely causes immediate failures, especially in large multi-pole (slow speed) motors. However, with a sufficiently degraded rotor, the machine may not able to develop the sufficient accelerating torque. Replacement of the rotor core in larger machine is costly and time consuming; therefore, by detecting anomaly in advance, such secondary deterioration can be prevented. Currently detection of anomalies is solved using frequency response of input current to the induction machine.
Accordingly, there is an ongoing need for improving upon accurately detecting rotor anomalies, or the onset of rotor anomalies.